The present invention relates generally to radio communication and, more particularly, to the format of transport channels and control channels within a frame of a radio communication system.
Radio communication systems conventionally multiplex data channels and control channels within a transmission frame. For example, Third Generation Partnership Project (xe2x80x9c3GPPxe2x80x9d) standardization for Wideband Code Division Multiple Access (W-CDMA) multiplexes three different data channels (e.g., transport channels) within a transmission frame of a fixed length. FIG. 1 illustrates a conventional frame format in accordance with the 3GPP standards. As shown, a frame 100 includes a first field A 105 for holding data associated with a first transport channel. The frame 100 additionally includes second fields B 115 and C 120 for conveying information associated with second and third transport channels, respectively. Because the A field 105 typically carries important information (e.g., in the case of voice coding, information that is most important for recreating intelligible speech), Cyclic Redundancy Check (CRC) bits 110 are additionally attached to the first field A 105 for providing error detection capability in connection with the first transport channel. The information carried by the B and C fields 115, 120 is typically of lesser importance, so these fields are not associated with CRC bits.
Each of the fields within the frame 100 shown in FIG. 1 may be designed to have a single, fixed beginning and ending location within the frame 100, thereby making each field easy to locate and decode. In this case, the length of each field must be large enough to accommodate the highest expected bit rate associated with the corresponding transport channel. Fixed field positions, however, use the system capacity in an inefficient way whenever a transport channel provides insufficient data to fill its associated field within the frame 100.
The use of variable field lengths (e.g., increasing or diminishing the length of the A, B, and/or C fields to accommodate more or less available data traffic) can alleviate the inefficiencies that can result from fixed field positions. For example, the length of the A field 105 is often permitted to be any one of a number of predefined lengths, thereby permitting information to be transmitted at a variable rate. To determine the actual length of a received A field 105, a process called xe2x80x9cblind rate detectionxe2x80x9d is used, in which the actual data rate is determined without the need for rate information to be expressly inserted into the frame. In one blind rate detection strategy, the receiver hypothesizes one of these predefined lengths, such as the shortest one. Using the hypothesized length, the A field 105 is decoded, and its CRC field 110 (which must, by definition, immediately follow the A field 105) determined. If the CRC field 110 indicates that no errors were detected, then the hypothesized length is presumed to have been correct. Otherwise, another one of the predefined lengths is hypothesized (e.g., the next largest length) and the process is repeated until a CRC field 110 indicates an absence of errors. At this point, the A field 105 is presumed to have been decoded correctly, and its length is known to be the last hypothesized length.
As mentioned earlier, fields B 115 and C 120 typically do not have attached CRC bits. Since, as defined in accordance with the 3GPP standards, the frame 100 is of a known length, the length of the B 115 and C 120 fields must be set to accommodate the length of the A field 105. Typically, for each of the predefined lengths of the A field 105, lengths for each of the B and C fields 115, 120 are predefined as well. Thus the lengths, as well as the starting positions, of the B and C fields 115, 120 are known once the length of the A field 105 is known.
In addition to the A 105, CRC 110, B 115 and C 120 fields described above, a variable length control channel DCCH is sometimes transmitted in the frame 100. Because it is transmitted only occasionally, it would be inefficient to define a frame format that always included the DCCH field. Consequently, the frame format is defined in a way that permits the DCCH field to xe2x80x9cstealxe2x80x9d bits from the C field 120. The DCCH field is also permitted to vary in length, however. This creates the problem of not knowing how many bits have been xe2x80x9cstolenxe2x80x9d from the C-field.
As shown in FIG. 2, it has been proposed to locate the DCCH field 203 (which includes an associated CRC field) at the end of the frame 200, with bits that make up the DCCH field 203 being xe2x80x9cstolenxe2x80x9d from the C field 201. The lengths of the A and B fields 105, 115 are determined in the same manner as described above. To determine the length of the C field 201, it is necessary to know the length of the DCCH field 203. In the proposal, this is done by hypothesizing a first one of the possible DCCH lengths (e.g., a shortest DCCH length), and decoding the DCCH field 203 from the end of the frame 200. This is illustrated in FIG. 2 by means of the backwards arrow 205. If the DCCH""s CRC field fails to detect any errors in the decoded result, then the hypothesized length of the DCCH field 203 is presumed to have been correct. Otherwise, another DCCH length is hypothesized, and the process is repeated until either the DCCH field 203 is correctly decoded, or until a failure to decode any DCCH field indicates that the DCCH field 203 is not present in the frame 200 (i.e., no bits were stolen from the C field 201). Once the length of the DCCH field 203 is known, the length of the C field can also be determined.
The proposed solution presents a number of problems. To begin with, it is very difficult to implement a format in which the bits are transmitted and received backwards. Furthermore, the proposed format is very different from other formats. This would require that a completely new kind of multiplexing be standardized.
It is therefore an object of the present invention to provide a multiplexing technique that permits a variable length DCCH field to be intermittently included in a frame having a fixed length.
In accordance with one aspect of the present invention, data is multiplexed in a frame having a fixed bit length in a telecommunication system. This is achieved by transmitting a first transport channel comprising a first number of bits; transmitting first error detection bits associated with the first transport channel and comprising a second number of bits; transmitting a second transport channel comprising a third number of bits; transmitting a third transport channel comprising a fourth number of bits; and selectively transmitting a control channel comprising a fifth number of bits. Furthermore, the control channel is transmitted after the first error detection bits and before transmission of the third transport channel; whenever the control channel is transmitted as part of the frame, a sum of the first, second, third, fourth and fifth number of bits equals the fixed bit length; and whenever the control channel is not transmitted as part of the frame, a sum of the first, second, third and fourth number of bits equals the fixed bit length.
In other aspects of the invention, the control channel may be transmitted between the first error detection bits and the second transport channel. Alternatively, the control channel may be transmitted between the second and third transport channels.
In another aspect of the invention, the fifth number of bits may further include error detection bits associated with the control channel.
In still another aspect of the invention, multiplexed data that is received as a frame in a telecommunication system is decoded, wherein the frame has a fixed bit length. This is achieved by decoding a first transport channel contained in the frame, wherein the decoding step includes determining a first length of the first transport channel; decoding a second group of bits having a second length that is a function of the first length; determining whether the second group of bits includes error detection bits associated with the second group of bits. Then, if the frame includes error detection bits associated with the second group of bits, then a third length and starting position of a second transport channel in the frame are determined, and the second transport channel is decoded, wherein the third length is a function of the first length and the second length. However, if the frame does not include error detection bits associated with the second group of bits, then the decoded second group of bits is used as the decoded second transport channel. Furthermore, the steps of decoding the first transport channel and decoding the second group of bits are performed in a same direction.
In another aspect of the invention, after decoding the first transport channel and prior to decoding the second group of bits, a third transport channel is decoded, wherein the third transport channel has a fourth length that is a function of only the first length.
Alternatively, the third transport channel may be decoded after decoding both the first transport channel and the second group of bits. In such embodiments, the third transport channel may have a fourth length that is a function of only the first length. Alternatively, the third transport channel may have a fourth length that is a function of both the first length and the second length.
In still other embodiments of the invention, data can be multiplexed in a frame having a fixed bit length in a telecommunication system by transmitting a first group of one or more transport channels, wherein the one or more transport channels in the first group together comprise a first number of bits; transmitting first error detection bits associated with one or more transport channels in the first group of one or more transport channels, wherein the first error detection bits comprise a second number of bits; transmitting a second group of one or more transport channels, wherein the one or more transport channels in the second group together comprise a third number of bits; transmitting a third group of one or more transport channels, wherein the one or more transport channels in the third group together comprise a fourth number of bits; and selectively transmitting a control channel comprising a fifth number of bits, wherein: the control channel is transmitted after the first group of one or more transport channels and the first error detection bits but before transmission of the third group of one or more transport channels; whenever the control channel is transmitted as part of the frame, a sum of the first, second, third, fourth and fifth number of bits equals the fixed bit length; and whenever the control channel is not transmitted as part of the frame, a sum of the first, second, third and fourth number of bits equals the fixed bit length.
In yet other alternative embodiments, multiplexed data that is received as a frame in a telecommunication system is decoded, wherein the frame has a fixed bit length. This is performed by decoding a first group of one or more transport channels contained in the frame, wherein the decoding step includes determining a first length of the first group of one or more transport channels; decoding a second group of bits having a second length that is a function of the first length; and determining whether the second group of bits includes error detection bits associated with the second group of bits. If the frame includes error detection bits associated with the second group of bits, then a third length and starting position of a second group of one or more transport channels in the frame is determined and the second group of one or more transport channels is decoded, wherein the third length is a function of the first length and the second length. If the frame does not include error detection bits associated with the second group of bits, then the decoded second group of bits is used as the decoded second group of one or more transport channels, wherein the steps of decoding the first group of one or more transport channels and decoding the second group of bits are performed in a same direction.